drm/msm/sde: move rotator start trigger to ctl start time

Trigger rotator start just before the CTL start.  Rotator start
should be triggered after the pipe flush bits have been set.

Change-Id: I7866990a88979783cd33d1b47f36796fb78a3d3c
Signed-off-by: Steve Cohen <cohens@codeaurora.org>